Now, I notice that ESR is typically from Quest whereas Labcorp seems to use Westgren Sedimentation Rate. The two measures do not seem to be identical: you could test at 1 on WSR but much higher on ESR. Do you know why that's the case?

1
Answers

ESR levels can be different from CRP in that it is a less specific marker of one's inflammatory condition as NON-inflammatory conditions like anemia, pregnancy, menstration, diet changes and medications can affect ESR.

Also, ESR is slower to react to inflammatory changes. So, if something is temporal in nature, and the inflammation subsides, the CRP will reflect the decrease in inflammation more quickly than the ESR, giving you results like you experience. That's why CRP is the first line lab to draw. But since you're going to get poked for the labs anyway, most providers will almost always order both and get as much data as possible.

Now an increase in one over the other is prognostic for certain pathologies when coupled with symptoms and other markers. SLE, for example, is associated with elevated ESR with a low CRP but it's usually not something that dubious.

Steroids would also cause that condition due to the slow response of ESR.

Now, I notice that ESR is typically from Quest whereas Labcorp seems to use Westgren Sedimentation Rate. The two measures do not seem to be identical: you could test at 1 on WSR but much higher on ESR. Do you know why that's the case?